As a starter, have a look at the video of the finished project, and keep on reading if you are interested.
I started the project with an Arduino Nano, the Chinese copies are around 5 euro these days. Then I realized that it would not fit in the box if I also had to include the 9V battery. So I switched to an AtTiny 85, a microcontroller from Atmel with a very small form factor and just 8 pins. They are ideal if your project is tight on space and/or budget and are easily programmable from the Arduino environment, just follow these instructions.
The Tiny must be fed at 5V, so I added the 7805 voltage regulator. Maybe a 78L05 would do, but the motor is eating more than 300mA when it is closing the switch and I felt more comfortable with the extra dissipation that the 7805 provides.
As a motor I am using a microservo. These kind of motors can turn 180 degrees and have a built in position control. They are really easy to wire: red cable for power, black or brown cable for ground and yellow cable to send the commands. Arduino has the <Servo.h> library which allows you to send commands directing the motor to a certain angle. If you are using the AtTiny, you will have to download and use <SoftwareServo.h> instead.
The shopping list
- A box, some 3 euro
- SG90 microservo, less than 4 euro at dealExtreme
- 9V battery and its connector
- microcontroller AtTiny 85, 1 to 1.5 euro at RS or other online shops
- Switch
- LED
- 7805 voltage regulator
- 4.7 and 0.1 microfarad capacitors
- 470 and 10K ohm resistors
The Schematics
or in a more realistic representation thanks to Fritzing:
The Arduino code
//Shannon Slow Detach Attiny85 // Carles Flotats, December 2013 // It reads the switch (pull upped). If activated, the led // is lit, the motor is moved from the STOPPOS degrees // starting position until the switch is off, the led is // unlit and the motor returns to POS degrees // Evolves from Shannon Complete Attiny85 to make it slower // by sending the degrees one by one // Detach evolution: to avoid inestability in the servo, // it is detached every time it finishes a movement //Shannon Machine on an AtTiny 85 #include <SoftwareServo.h> // has been modified from the downloaded one to use Arduino.h // instead of Wsomething.h // If you are using an Arduino instead of an AtTiny, you better use <Servo.h> SoftwareServo myservo; // create servo object to control a servo int switchVal=1; //variable to store the state of the switch int ledPin=2; // pin 2, output to the resistor and the status led int servoPin=1; // pin 1, output to the servo control, yellow cable int switchPin=0; // pin 0, input from the switch, pull up configuration int stopPos=53; // position in degrees of the motor while resting int currentPos=stopPos; void setup() { myservo.attach(servoPin); // attaches the servo on pin 9 to the servo object myservo.write(stopPos); // initialize the servo to the stop position for (int i=0; i <= 20; i++){ // softwareServo::refresh must be executed // every 50 ms to avoid unstabilization delay(25); SoftwareServo::refresh(); } myservo.detach(); pinMode(ledPin, OUTPUT); pinMode(switchPin, INPUT); digitalWrite(ledPin, LOW); } void loop() { while (switchVal==1){ //if the switch is not activated, the loop is switchVal=digitalRead(switchPin);// not broken and the rest of the program is not executed delay(15); } //end of while digitalWrite(ledPin, HIGH); delay(500); myservo.attach(servoPin); while (switchVal==0){ currentPos=currentPos++; myservo.write(currentPos); delay(10); SoftwareServo::refresh(); switchVal=digitalRead(switchPin); } // end of while digitalWrite(ledPin, LOW); currentPos=stopPos; for (int i=0; i <= 20; i++){ //softwareServo::refresh must be executed every 50 ms to avoid unstabilization delay(25); SoftwareServo::refresh(); } //end of for myservo.write(stopPos); for (int i=0; i <= 40; i++){ //softwareServo::refresh must be executed every 50 ms to avoid unstabilization delay(25); SoftwareServo::refresh(); } //end of for myservo.detach(); switchVal=1; } // end of loop
